The present invention relates generally to process chambers and, more particularly, to a getter system for purifying the confinement volume in process chambers.
Thin layers of metallic or ceramic materials deposited by, e.g., physical vapor deposition (PVD), which is also referred to as xe2x80x9csputtering,xe2x80x9d are used in a variety of applications. For example, in the semiconductor industry, a number of layers are deposited by PVD and then selectively removed in the fabrication of integrated circuits. In the compact disc and digital versatile disc (DVD) industries, the reflective layer of aluminum is deposited by PVD.
The processes used to deposit such thin layers require the use of high purity gases. In particular, in the fabrication of semiconductors, impurities in the process gases may result in microflaws in the electronic devices. In general, the smaller the size of the device, the greater the effect such microflaws have on the operability of the device. In light of the continuing trend to reduce the average size of electronic devices, the use of increasingly pure process gases is required to obtain an acceptable yield percentage.
A common practice in the semiconductor industry for purifying gases upstream of a process chamber, e.g., a PVD process chamber, is the use of getter materials in combination with conventional pumps. Even when the purity of the inlet gases is controlled, however, impurities may be introduced in the chamber as the result of the degassing of the materials forming the walls or other parts of the chamber. For example, contamination is a significant problem in the deposition of aluminum and titanium nitride layers. In the sputtering process typically used to deposit such layers, the flat surface of a target, which consists of the material to be deposited, is eroded by the impact of ions of heavy atoms, e.g., Ar+ ions, that have be accelerated by a suitable electric field. The particles removed from the surface of the target are deposited in the form of thin layers onto the substrate of semiconductor material, which faces the target and is generally arranged so as to be parallel to the surface of the target. During the sputtering process, the gases within the target, e.g., gases mechanically incorporated into the structure of the material during production, are discharged and result in a high concentration of impurities in the confinement volume. The most common impurities are H2O, H2, CO, CO2, and CH4, and the concentration of these impurities may range, depending upon the specific features of each deposition process, from about 1 ppm to about 100 ppm.
International Publication Nos. WO 96/13620, WO 96/17171, and WO 97/17542, European Publication No. 0 693 626, and U.S. Pat. No. 5,778,682 to Ouellet disclose in situ getter pump systems for purifying gases arranged inside process chambers, e.g., PVD chambers. These in situ getter pump systems are disposed within the process chambers at locations outside of the confinement volume. One of the main advantages of such an in situ getter pump system is that it substantially reduces the pump down time required for the chamber to reach acceptable vacuum and impurity levels after the chamber has been opened, e.g., for maintenance operations.
The in situ getter pump systems disclosed in the above-listed references do not fully solve the problem of impurities within the confinement volume during PVD operations because this volume is defined by screens that prevent the target material from being deposited onto undesired portions of the chamber, e.g., feedthroughs, openings for connecting the chamber to gas lines, etc. These screens significantly reduce the gas conductance between the confinement volume and the remaining volume of the chamber and thereby create two different gaseous atmospheres within the processing chamber. As a result of this reduced gas conductance, the sorption of impurities in the confinement volume by the in situ getter pump systems disclosed in the above-listed references is negligible. Thus, the problem of effectively purifying the gaseous atmosphere within the confinement volume during PVD operations so that contamination of the deposited layers is avoided remains unsolved.
In view of the foregoing, there is a need for a mechanism that effectively purifies the gaseous atmosphere within the confinement volume of a process chamber, e.g., a PVD chamber, such that contamination of the deposited layers is avoided.
Broadly speaking, the invention fills this need by providing a getter system for purifying the gaseous atmosphere within the confinement volume of a process chamber, e.g., a PVD chamber. The getter system includes one or more substantially planar getter devices that are arranged so as to be substantially parallel to and spaced apart from the screens that define the confinement volume.
In one aspect of the invention, a getter system for use in a process chamber having at least one screen that defines a confinement volume is provided. The getter system includes at least one substantially planar getter device disposed within the confinement volume such that the at least one getter device is substantially parallel to and spaced apart from the at least one screen. The at least one getter device has an inner surface facing the at least one screen and an outer surface facing the confinement volume, with at least the inner surface being comprised of getter material. The at least one getter device is spaced apart from the at least one screen such that the inner surface and the at least one screen define an inner space that is in gas flow communication with the confinement volume.
The outer surface of the at least one getter device preferably occupies about 70% to about 99%, and more preferably about 80% to about 95%, of the available surface area. This may be accomplished by using multiple getter devices that are arranged so that they are not in contact with one another or by using one or more getter devices that are discontinuous. The distance between the inner surface of the at least one getter device and the at least one screen is preferably in a range from about 1 mm to about 5 cm.
The at least one getter device may be formed of a variety of getter materials. Suitable getter materials include but, are not limited to Zr, Ti, Nb, Ta, V, alloys thereof, and alloys containing one or more of Zr, Ti, Nb, Ta, and V and one or more of Cr, Mn, Fe, Co, Ni, Al, Y, La, and rare earths. Preferred getter materials include an alloy containing 84 wt % of Zr and 16 wt % of Al, an alloy containing 70 wt % of Zr, 24.6 wt % of V, and 5.4 wt % of Fe, an alloy containing 84 wt % of Zr and 16 wt % of Al and at least one of Zr and Ti, and an alloy containing 70 wt % of Zr, 24.6 wt % of V, and 5.4 wt % of Fe and at least one of Zr and Ti.
In one embodiment the at least one getter device is a body obtained by sintering powdered getter material. In another embodiment the at least one getter device is comprised of getter material deposited onto a metal support. The metal support is preferably comprised of a nonferromagnetic material such as, for example, steel or a nickel-chromium alloy. The metal support preferably has a thickness in a range from about 0.1 mm to about 1 mm. The deposit of getter material preferably has a thickness in a range from about 20 xcexcm to about 500 xcexcm.
In another aspect of the invention, a process chamber for physical vapor deposition is provided. The process chamber includes a housing and a substrate support disposed within the housing. A target is disposed within the housing such that the target faces the substrate support. At least one screen is disposed within the housing and defines a confinement volume that extends between the target and the substrate support. A getter system is disposed within the confinement volume.
In one embodiment the getter system includes at least one substantially planar getter device disposed within the confinement volume such that the at least one getter device is substantially parallel to and spaced apart from the at least one screen. The at least one getter device has an inner surface facing the at least one screen and an outer surface facing the confinement volume, with at least the inner surface being comprised of getter material. The at least one getter device is spaced apart from the at least one screen such that the inner surface and the at least one screen define an inner space that is in gas flow communication with the confinement volume.
The getter system of the present invention effectively purifies the gaseous atmosphere within the confinement volume of a process chamber. This significantly reduces contamination of the thin layers being deposited and thereby increases the efficiency with which such layers may be produced. The getter system of the present invention is particularly advantageous in the deposition of titanium, which is a well known getter material. During the deposition process, some of the titanium is deposited on the screens that define the confinement volume. The extent to which the titanium deposited on the screens sorbs hydrogen is significantly reduced because the getter system of the invention effectively sorbs hydrogen and other impurities from the confinement volume of the process chamber. As a result, the titanium deposited on the screens does not flake off in the form of metal microlayers and contaminate the thin film of titanium being deposited on the substrate. Thus, the getter system of the invention increases the efficiency with which thin layers of titanium may be deposited.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.